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Area Forecast Discussion

144
FXUS64 KHUN 280259
AFDHUN

Area Forecast Discussion
National Weather Service Huntsville AL
959 PM CDT MON JUN 27 2016

.UPDATE...
Evening update to public forecast.

&&

.DISCUSSION...
Latest radar data suggests that coverage of residual light rain in
the wake of afternoon convection continues to dissipate this
evening, and POPs will be lowered for majority of the region for the
remainder of the night. That said, we will need to closely monitor
the progress of a small backward propagating MCS currently across
northern portions of the Cumberland Plateau in TN. Short term models
suggest that sfc-850 mb flow will gradually veer throughout the night
a 500-mb trough axis advances southeastward through the region, and
this may be sufficient to sustain this MCS for several more hours.
Although bulk of the convection will likely remain to the east of our
forecast area, we will maintain a slightly higher prob for both
showers and thunderstorms in ne Alabama and southern TN. Weak ascent
associated with the 500-mb trough may be sufficient for a few
sprinkles or patches of light rain in remainder of the region, and a
20% POP will be included for rest of the forecast area. Otherwise, a
nearly saturated boundary layer and light flow regime will be
favorable for more widespread fog formation early Tuesday morning,
with areas of fog possible. Visibility should be confined to the 3-5
mile range, however, due to impacts from a lingering deck of
altostratus clouds. Temps/dewpoints and winds look good with no
changes required.

70/DD

&&

.AVIATION...
(Issued 706 PM CDT MON JUN 27 2016)
For 00Z TAFs: Although primary axis of tsra has now shifted well to
the se of MSL/HSV, residual -ra will continue at each terminal for
a few hrs early this evening. This should not have a significant
impact on airport operations with vsbys expected to remain aoa 6 sm
and cigs expected to be aoa 7 kft, but we did include -ra as
prevailing wx cond thru 28/04Z. Ovc altostratus layer will persist
for remainder of the night, but still expect fairly widespread br/fg
to develop shortly after pcpn ends arnd 04Z. Prevailing vsbys should
remain in the 3-5 sm range, with periodic drops to arnd 2 sm btwn
07-11Z. Conds will improve after 13-14Z as nne flow strengthens and
drier air pushes into the region. Higher probs for storms tomorrow
will be south of the TN River, so we will include no pcpn in either
TAF attm.

70/DD

&&

.PREV DISCUSSION...
(Issued 706 PM CDT MON JUN 27 2016)
(Issued 223 PM CDT MON JUN 27 2016)
At 19z, showers and thunderstorms were continuing to develop and
overspread the forecast area from the west and northwest along and
ahead of a convergent boundary/pre-frontal trough. This boundary was
extending southwest out of middle Tennessee into north Mississippi.
Dewpoint temps ahead of the storms had increased into the low-mid 70s
except for northeast Alabama, where the lower atmosphere had mixed
out a bit with dewpoint temps there in the upper 60s. Will continue
into the evening with likely to occasional shra/tsra and will slowly
lessen pops with time into the overnight hours as the RAP/HRRR and
Hi-Res short term models indicate that there should be some
subsidence that will move southeast into the area behind the initial
band of shra/tsra across the area.

The short term models are indicative that the main cold front should
shift southeast into middle Tennessee by 12z Tuesday and through the
southern portions of the forecast area by 18z Tuesday. Will maintain
low chance pops for Tuesday due to the proximity of the cold front to
the forecast area. Expecting that afternoon heating/instability and
still decent PWAT values above an inch, should contribute to at least
low chance pops across the region. The cold front is progged by the
models to be well south of the forecast area by Tuesday night with
high pressure building southeast out of the midwest toward the
Tennessee valley.

A mid to upper level northwest flow aloft will result in dry and
cooler weather for the forecast area through Thursday. Both the GFS
and ECMWF models are in similar agreement involving the southeast
movement of the next cold front through the midwest. The upper flow
is expected to become also more zonal by Friday as a short wave is
expected to move slowly east-southeast through the southern plains
along the frontal boundary. Will slowly increase pops into the chance
category by Saturday as the frontal boundary and short wave get a
little closer to the forecast area. By Saturday, the ECMWF model
indicated that the frontal boundary should stall out over middle
Tennessee, while the GFS model characteristically indicated that the
cold front would make it into north Alabama. Will follow closer to
the more conservative ECMWF model involving the frontal placement.
The nearly stationary cold front is expected to slowly shift
southward to close to the forecast area by Sunday and have gone with
higher chance pops from Sunday through Monday. As far as temps are
concerned, will trend more toward the slightly cooler GFS temps
through the extended forecast periods.

TT

&&

.HUN Watches/Warnings/Advisories...
AL...NONE.
TN...NONE.
&&

$$

For more information please visit our website
at weather.gov/huntsville.



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